"Compared with spontaneous conceptions in couples with no record of infertility, singleton babies from assisted conception were almost twice as likely to be stillborn, more than twice as likely to be pre-term, almost three times as likely to have very low birth weight, and twice as likely to die within the first 28 days of birth," said study leader Professor Michael Davies, from the University of Adelaide's Robinson Institute.

"These outcomes varied depending on the type of assisted conception used. Very low and low birth weight, very pre-term and pre-term birth, and neonatal death (infant death) were markedly more common in births from IVF and, to a lesser degree, in births from Icsi.

"Using frozen embryos eliminated all significant adverse outcomes associated with Icsi but not with IVF. However, frozen embryos were also associated with increased risk of macrosomia (big baby syndrome) for IVF and Icsi babies."

Significantly, the study also looked at birth outcomes for women who found it hard to get pregnant but never received intensive fertility treatment.

Their chances of experiencing complications were much higher than average.

"Women in this group who eventually conceived without the help of invasive assisted reproduction gave birth to babies who were nine times more likely to have very low birth weight, seven times more likely to be very pre-term, and almost seven times more likely to die within the first 28 days of birth," said Prof Davies.

"This may be due to the underlying medical conditions related to their infertility, or the use of fertility medications or therapies that are not recorded."

Fertility expert Dr Dagan Wells, from Oxford University, said this finding indicated that fertility treatment may not be to blame for the higher risk of birth problems seen in patients.

"Perhaps the most striking finding is that rates of prematurity, low birth-weight and infant death were highest of all for couples who had a fertility problem but eventually succeeded in conceiving without the help of IVF," said Dr Wells.

"This suggests that the problems seen for babies born after IVF may be related to the patient's infertility rather than the treatment itself. In fact, for couples with reduced fertility, IVF seemed to lessen these risks compared to natural conception."

He added: "It is very important that patients are provided with useful information concerning the risks as well as the benefits of any medical interventions they might undertake so that they can make an informed decision about whether a given procedure is right for them.

"Although this study suggests that some adverse outcomes are higher in pregnancies conceived using IVF, it is important to understand that the overall risk of these problems remains low. As such, I doubt these findings will deter many infertile couples from using IVF."

Sheena Lewis, professor of reproductive medicine at Queen's University, Belfast, agreed. She said: " We have known for some time that couples conceiving spontaneously after a period of infertility have poorer outcomes. This indicates that these problems may come from the disease rather than the fertility treatment.

"Also a very positive finding in this study is that the use of frozen embryos eliminates all the adverse outcomes following Icsi. Freezing embryos is a routine procedure in fertility clinics and may be a useful option for those couples concerned about these findings."

The research is published in the online journal Public Library of Science ONE.